Samsung is facing allegations that a supplier used child labour. Photograph: Bloomberg

Samsung is facing a fresh accusation that one of its Chinese suppliers hired children to meet production targets during a period of high demand from the South Korean electronics giant.

Samsung Electronics said on Thursday it is looking into the allegation by China Labor Watch that a supplier, Shinyang Electronics in Dongguan, Guangdong province, hired children and student workers under the legal working age.

The accusation conflicts with Samsung's recent report on conditions at suppliers. It said no child labour was found by an external audit last year of about 100 Chinese suppliers. That audit found 59 suppliers that did not provide safety equipment to employees. It also said excessive working hours were common.

At the time, Samsung promised to eliminate illegal overtime and other violations. It began to detail its efforts to remove child workers, introducing a new hiring process with strict identity checks at its suppliers in China. Samsung said it would sever its relationship with companies that failed to abide by its code of conduct.

There are hundreds of Samsung suppliers in China.

Citing its latest finding, China Labor Watch said Samsung's audit showing there was no child labour was inaccurate. Li Qiang, the watchdog's executive director, said Samsung's reports are meant to reassure investors and don't have any value for workers. "Samsung's monitoring system is ineffective and has failed to bring about improvements for workers," he said.

Samsung said that, with a third party auditor, it conducted three inspections of Shinyang Electronics in 2013 and 2014 but did not find evidence of child labour. It reiterated that it has zero tolerance for child labour.